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Review Article

Carbon monoxide (CO) is a colourless, odourless andtasteless gas. It is normally present in the atmosphere in aminiscule concentration (<0.001%). Carbon monoxidechemically consists of one atom of carbon and oxygen.This is in contrast to carbon dioxide which is relativleyabundant in the atmosphere (0.035%) and each moleculeof carbon dioxide consists of carbon and two oxygenatoms. Both the gases i.e., carbon monoxide and carbondioxide are produced as a result of combustion ofhydrocarbon fuels and organic matter (Organic matterrefers to things made of hydrogen and carbon, which whenburnt in presence of oxygen result in formation of carbondioxide). It is important to note here that incomplete orpartial combustion i.e., combustion that occurs at placeswhich have limited oxygen in the atmosphere, results incarbon monoxide formation which as already delineatedabove has only one oxygen atom, rather than formation ofthe relatively less toxic carbon dioxide. Whenever any fuelsuch as gas, oil, kerosene, wood, or charcoal is burnt, thesegases are generated.

If appliances that burn fuel are maintained and usedproperly, the amount of CO produced is usually not

hazardous. However, if appliances are not workingproperly or are used incorrectly, dangerous levels of COcan result. Hundreds of people die accidentally every yearfrom CO poisoning caused by malfunctioning orimproperly used fuel-burning appliances, or by idlingcars [1].

CO POISONING SYMPTOMS [2]

CO is an asphyxiant gas and its accumulation resultsin a varied constellation of symptoms because of itsaffinity for hemoglobin with which it combines formingcarboxyhemoglobin (COHb) and disrupting oxygentransport. CO poisons by entering the lungs via breath anddisplaces oxygen from the blood stream. Interruption ofthe normal supply of oxygen puts at risk the functions ofthe heart, brain and other vital organs. Tissues with thehighest oxygen needs — myocardium, brain, andexercising muscle — are the first affected. Unbornchildren, infants and small children, expectant mothers,elderly people, and people with anemia or with ahistory of heart or respiratory disease are especiallysusceptible.

CARBON MONOXIDE POISONING

Anupam Prakash*, SK Agarwal** and Nirupam Prakash***

*Assistant Professor, Department of Medicine, Lady Hardinge Medical College & Smt. S.K. Hospital, New Delhi 110 001, India.**Consultant Internal Medicine and Academic Advisor, Indraprastha Apollo Hospitals, Sarita Vihar, New Delhi 110 076, India,

*** Senior Medical Officer, Department of Posts, Lucknow, India.

Correspondence to: Dr. Anupam Prakash, Assistant Professor, Department of Medicine, Lady Hardinge Medical College &Smt. S.K. Hospital, New Delhi 110 001, India.

Carbon monoxide is a colourless, odourless and tasteless gas existing in a miniscule concentration in theatmosphere (< 0.001%), and is a product of partial combustion. Carbon monoxide poisoning is associated witha high incidence of morbidity and mortality. Symptoms are usually non-specific and include fatigue, headache,dizziness, nausea and vomiting, cognitive impairment, and tachycardia; mimicking an influenza-like illness.Symptoms occurring in more than one person (belonging to the same family/office) simultaneously and therelief also occurring at the same point of time in them should sound the physician’s mind for suspected carbonmonoxide poisoning. A high index of suspicion and presence of a source of generation of carbon monoxide arethe diagnostic aids which can be confirmed by blood carboxyhaemoglobin levels. Removal from the source ofcarbon monoxide generation, moving the person to fresh air immediately is most important. In the emergencyroom, oxygen therapy is the key. Immediate treatment with a high fraction of inspired oxygen and carefulclinical evaluation are mandatory for effective management. Patients with a carboxyhaemoglobin level of 10%or more should always be treated and 100% oxygen for 8 hours is recommended for patients requiring artificialventilation. Hyperbaric oxygen also holds promise in select cases specially those with a history ofunconsciousness, cardiovascular instability or ischemia, persistent mental and/or neurologic deficits andprobably in pregnant patients.

Key words: Carbon monoxide, Asphyxiant, Poisoning, Hyperbaric oxygen.

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Review Article

33 Apollo Medicine, Vol. 7, No. 1, March 2010

angeethis in rooms whether it be palatial buildings, urbanslums or rural villages. Kitchens are also vulnerable withthe use of cooking gas ranges, ovens, wood stoves,chulhas etc., more so in the modern apartments, whereinthere is no proper ventilation and obviously no space forchimneys. If the flame of your gas appliances is orange,you should get it cheked, since it indicates you aregenerating more CO, although a blue flame does notalways mean you are safe. Exhausts in kitchens are a mustand should always be switched on when working inkitchens. With increasing usage of the heating filamentsand space heaters in our country, specially in ill-ventilatedhouses, chances of CO poisoning are going to increase.Blocked furnace or blocked chimneys only add to the risk.

Idling vehicles in garages are also a potential source ofthis lethal gas and the concentrations/fumes can build upvery rapidly despite the garage doors being open. Avehicle left on in an attached garage can potentially allowCO to seep into the house and cause poisoning.

Cases have occurred wherein the heating filaments inhouses have been inadvertently left on and the central airconditioning was also on, the ducts of the latter acted asconduits for the spread of lethal carbon monoxidegenerated by the former resulting in deaths of all familymembers of a household.

Persons, tired of sleepless nights due to power cuts,have died while sleeping in the comfort of theirairconditioned cars parked in their garages, because of thecontinuous combustion of petrol/diesel resulting ingeneration of carbon monoxide which is sucked into theinside of the car by the airconditioner fan which sends incool air harbouring the lethal gas. Driving slowly in heavytraffic with the airconditioner on and the windows tightlyshut also predisposes to chances of CO poisoning. Thecar’s exhaust system needs to be checked periodically.

People who use a gas oven to heat their home or usinga charcoal grill indoors, even though in a fireplace arethrowing an open invitation to “Lord Yama”. Persons whosleep in any room with an unvented gas or kerosene spaceheater are also exposing themselves to undue risk.Generators should always be positioned in the openverandah, though they may be covered to prevent climaticadversities. Use of gasoline-powered engines (mowers,weed trimmers, small engines or generators) in enclosedspaces, again increases the risk of CO poisoning manifold.

WHEN TO SUSPECT CO POISONING?

A high index of suspicion is required [3,4]. Symptomsoccurring only in particularly closed surroundings andimproving if the person moves out of that place,

Symptoms may be non-specific and include fatigue,headache, dizziness, nausea and vomiting, cognitiveimpairment, and tachycardia, whch may mimic influenzaor viral illness. However, the entire family having similarsymptoms, specially at the same time should promptsuspicion of CO poisoning. CO exposure shortens time toonset of angina in exercising individuals with ischemicheart disease and decreases exercise tolerance in thosewith chronic obstructive pulmonary disease (COPD).

The formation of carboxyhaemoglobin in thecirculation depends upon the duration of exposure to COand its concentration in the atmosphere. Greater is theconcentration and longer the exposure, greater is theamount of COHb formed in the circulation. The higher thelevels of COHb, greater are the symptoms and moreadverse health effects.

At levels of 2.3-4.3% COHb in blood, time toexhaustion in exercising healthy men is reduced and at2.9-4.5%, reduced exercise capacity is noted in patientswith angina and the duration of angina attacks isprolonged. However, below 5% no decrements inconcentration or constituional symptoms are seen.Between 5-17%, there is dimninution of visual perception,manual dexterity, learning ability, deterioration inperformance of sensorimotor tasks as in driving is noted.As levels rise to about 30%, headache, fatigue andimpaired judgement are noted. Since many of thesesymptoms are similar to those of viral illnesses/flu, foodpoisoning, or other illnesses, possibility of CO poisoningcould be missed easily, specially in tropical countries likeIndia. At 40% confusion sets in while loss ofconsciousness occurs at 60%. Death occurs at 80%concentration or even at lower concentrations if theexposure continues for long.

The safety level for the concentration of CO in the airis 50 parts per million (ppm). A concentration of 200 ppmcan cause slight headache within 2-3 hours; at 400 ppm,frontal headache occurs with in 1-2 hours, becomingwidespread in 3 hours; while at 800 ppm dizziness,nausea, convulsions occur in 45 minutes and the patientmay be unconscious in 2 hours. Average levels in homeswithout gas stoves vary from 0.5 to 5 ppm. Levels nearproperly adjusted gas stoves are often 5 to 15 ppm andthose near poorly adjusted stoves may be 30 ppm orhigher.

Real-life situations

Cases of CO poisoning have occurred with use ofheaters in closed rooms, use of gas stoves or oil stoves insmall unventilated or less ventilated rooms, and use of

Review Article

Apollo Medicine, Vol. 7, No. 1, March 2010 34

reappearing on returning back should arouse suspicion.The surroundings could be house, garage or workplaceeven.

Symptoms occurring in more than one person [5], maybe family members or at the work place, simultaneouslyand the relief also occurs at the same point of time in all.

This point requires close attention and the person hasto strain his brains to answer it. Do the symptoms occur ina closed place and does that place have even a remotechance of having a fuel-burning appliance?

COHb levels can be measured in blood and thediagnosis confirmed.

MEASURES TO BE TAKEN IF CO POISONING IS

SUSPECTED

Get fresh air immediately. Open all doors andwindows, turn off combustion appliances and move out inthe free air, as soon as possible.

Consult your doctor immediately and tell him that yoususpect CO poisoning, even if he does not suspect it. In anemergency, administering oxygen is helpful since it bindsto haemoglobin forming oxyhaemoglobin displacingcarbon monoxide from carboxyhaemoglobin, and rapidlyreversing symptoms. Oxygen therapy is the key treatmentof carbon monoxide poisoning and hyperbaric oxygen hasbeen shown to interdict and improve the clinical outcomein some patients specially those with a history ofunconsciousness, cardiovascular instability or ischemiaand persistent mental and/or neurologic deficits.

Immediate treatment with a high fraction of inspiredoxygen and careful clinical evaluation are mandatory foreffective management [6]. In a recent paper, it isrecommended that patients with a carboxyhaemoglobinlevel of 10% or more should always be treated and 100%oxygen for 8 hours was recommended for patientsrequiring artificial ventilation. It was even recommendedthat hyperbaric oxygen can be considered for pregnantpatients [7].

REFERENCES

1. Varon J, Marik PE, Fromm RE Jr, Gueler A. Carbonmonoxide poisoning: a review for clinicians. J EmergMed 1999; 17: 87-93.

2. Kao LW, Nanagas KA. Toxicity associated with carbonmonoxide. Clin Lab Med 2006; 26: 99-125.

3. Kao LW, Nanagas KA. Carbon monoxide poisoning. MedClin North Am 2005; 89: 1161-1194.

4. Kao LW, Nanagas KA. Carbon monoxide poisoning.Emerg Med Clin North Am 2004; 22: 985-1018.

5. Sadovnikoff N, Varon J, Sternbach GL. Carbon monoxidepoisoning. An occult epidemic. Postgrad Med 1992; 92:86-96.

6. Hardy KR, Thorn SR. Pathophysiology and treatment ofcarbon monoxide poisoning. J Toxicol Clin Toxicol 1994;32: 613-629.

7. de Pont AC. The guideline ‘Treatment of acute carbon-monoxide poisoning’ from doctors in clinics with a tankfor hyperbaric ventilation (Article in Dutch). Ned TijdschrGeneeskd 2006; 150: 665-669. (Abs).

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